Enos being prepared for insertion into the Mercury-Atlas 5 capsule in 1961.

Enos was brought from the Miami Rare Bird Farm on April 3, 1960. He completed more than 1,250 training hours at the University of Kentucky and Holloman Air Force Base. Training was more intense for him than for his predecessor Ham, because Enos was exposed to weightlessness and higher gs for longer periods of time. His training included psychomotor instruction and aircraft flights.

Enos was selected for flight only three days before launch. Two months prior, NASA launched Mercury Atlas 4 on September 13, 1961, to conduct an identical mission with a "crewman simulator" on board. Enos flew into space aboard Mercury Atlas 5 on November 29, 1961. He completed his first orbit in 1 hour and 28.5 minutes.[1]

Enos was scheduled to complete three orbits, but the mission was aborted after two due to two issues: capsule overheating and a malfunctioning "avoidance conditioning" test subjecting the primate to 76 electrical shocks. The capsule was brought aboard the USS Stormes (DD-780) in the late afternoon and Enos was immediately taken below deck by his Air Force handlers. The Stormes arrived in Bermuda the next day.

Enos's flight was a full dress rehearsal for the next Mercury launch on February 20, 1962, which would make Lt. Colonel John Glenn the first American to orbit Earth, after astronauts Alan Shepard, Jr. and Gus Grissom's successful suborbital space flights. On November 4, 1962, Enos died of shigellosis-related dysentery, which was resistant to then-known antibiotics. He was constantly observed for two months before his death. Pathologists reported no symptoms that could be attributed or related to his previous space flight. Many believe Enos's remains were dissected like Ham, who was extensively studied postmortem at the Armed Forces Institute of Pathology. Some of Ham's remains, minus the skeleton (which remained with AIP), were buried at the International Space Hall of Fame in New Mexico. Recent attempts by space scholars to locate Enos's remains were unsuccessful. Some confirmed post-mortem study was undertaken, but no evidence of final disposition has been found. Enos's body may have been discarded when examinations completed.[citation needed].